This invention is directed to an improved non-rotating plug set for use in cementing the casing in well bores.
Previously, a plug set and the residual cement in the casing cemented in a well bore were removed by drilling operations using tooth-type rock bits. The teeth on the rock bit proved effective in the drilling of the plug set, even though the individual plugs of the plug set were free to rotate with respect to each other and the floating equipment.
However, with the advent of polycrystalline diamond compact (PDC) drill bits to drill out the plug set and the residual cement in the casing cemented in a well bore it has become necessary to use a non-rotating plug set during the well casing cementing process to facilitate the drilling of the plug set and residual cement. For whatever reasons, the teeth on the PDC drill bit does not as effectively drill through the conventional plug set used in casing cementing operations as the conventional tooth-type rock bit. However, with the use of a non-rotating plug set in casing cementing operations, the PDC drill bit can drill through the plug set, residual cement and floating equipment in time periods comparable to that of conventional tooth-type rock bits.
A prior art non-rotating plug set as set forth in U.S. patent application Ser. No. 07/272,608, filed on Nov. 16, 1988, utilizes an insert in the upper plug of the plug set which has a portion thereof engaging recesses in a portion of the lower plug and an insert in the lower plug to abut a portion of a piece of conventional floating equipment.